The use of man-operated trolleys provided with one or more self-steering wheels has a number of advantages given that a user can steer the trolley in any direction by pushing or pulling it from a push bar or handle provided for such purpose. However, and especially when all the wheels of the trolley are self-steering wheels, certain situations present themselves in which the handling of the trolley is very problematic. For example, when the ground has an inclination in a direction that is transverse to forward movement direction of the trolley, the latter tends to move to the side instead of in a straight line, or when the direction of the front wheels is to be changed by acting on a push bar located at the rear end of the trolley, the latter tends to maintain the previous path though with the trolley turned. Any of these situations is worsened when the trolley is full.
These difficulties cold be lessened if at least one of the wheels of the trolley, preferably a front wheel, could be guided by the user.
Patent document WO 92/10388, with priority date May 12, 1990, discloses a device for the guiding of a trolley provided with self-steering wheels.
Patent EP-A-0701939, with British priority date Sep. 19, 1994, discloses a supermarket trolley comprising a control device for self-steering wheels and a protective rim for the basket.
U.S. Pat. No. 3,190,386, granted on Jun. 22, 1965, describes a motorized supermarket trolley that can be steered and nested together with other similar trolleys. In this case, the trolley includes a double wheel actuated by an electric motor through a transmission.
Patent application ES-A-2153729, filed by the applicant of this document on Nov. 2, 1998, discloses a human-powered trolley comprising a frame, a push bar and wheels, at least one of which is a self-steering wheel. The trolley further includes handles, preferably integrated in a single body, hingedly mounted on the mentioned push bar, which is hollow. The handles are connected to corresponding cables which, passing through the inside of the push bar and other elements of the frame, reach a pulley associated to the rotating fork supporting one of the self-steering wheels. Thus, the wheel pivots in terms of its orientation in response to the movements of the handles. A connecting bar is provided between a crank associated to the supporting fork of the actuated wheel and another crank associated to the supporting fork of another self-steering wheel to make them pivot in unison.
This arrangement has proven to be fully satisfactory in practice in terms of the guiding of a self-steering wheel. However, neither in this patent application ES-A-2153729 belonging to the current applicant nor in the previously mentioned documents WO 92/10388 and U.S. Pat. No. 3,190,386 the possibility of disconnecting the steering members at will is provided so as to allow the free self-steering operation of the wheel. In contrast, the wheel involved is permanently controlled by the steering members, which prevents, for example, a side movement of the trolley. Furthermore, given that this type of self-steering wheel, due to its very construction, is mounted in a support that is able to pivot in relation to a vertical axis shifted from the center of the wheel, or in other words, shifted from the point of contact of the wheel with the ground, the wheel tends to be located behind said vertical axis in relation to the forward movement direction. All the mentioned devices have the steering members mounted in relation to the wheel considering a predetermined forward movement direction. When the trolley is pushed or pulled in a backwards direction, or in a direction opposite to the mentioned predetermined forward movement direction, the wheel connected to the steering members tends to be located in the opposite side of the vertical axis of its support, forcing the mechanism to a point that is beyond the functions it is provided for.
Furthermore, the unisonous guiding of two wheels of the trolley mounted in parallel has a problem insofar as each of them should follow a path with a different radius of curvature, for which purpose each of the wheels would have to pivot variably with a different angle, which is impossible to implement by guiding one of the wheels and having a simple connecting rod to the other wheel. This makes one of the wheels skid in curved paths. In fact, it has been found that the guiding of only one of the wheels is sufficient when the other one is freely self-steering.
Another problem with U.S. Pat. No. 3,190,386 and the mentioned patent application ES-A-2153729 is in relation to the hysteresis of flexible mechanical transmissions, especially using Bowden cable. Indeed, flexible cables as well as their corresponding cable guides, supporting elements, levers, etc., have a certain elasticity that accumulates in the system causing, in addition to considerable loss of efficiency between the drive element and the follower element, an unpleasant sensation of a lack of promptness in response to the steering members.
In addition, patents ES-A-8704020 and U.S. Pat. No. 5,131,517 disclose respective coin-operated locking devices for immobilizing trolleys.
Upon analyzing the background documents mentioned above, it can be deduced that there is a need for a device for guiding at least one self-steering wheel of a trolley with a locking device that can optionally be coupled/uncoupled by the user. Another need is to provide a transmission that is preferably flexible, which prevents, at least in part, the aforementioned hysteresis problem.